This invention generally relates to the field of intravascular catheters and particularly balloon catheter suitable for coronary angioplasty procedures,
PTCA, which is now one of the most widely used treatment modalities for heart disease, basically comprises advancing a dilatation catheter, having an inflatable balloon on its distal extremity, into the patient's coronary anatomy, usually over a guidewire, until the balloon of the dilatation catheter is properly positioned across the lesion to be dilated. Once properly positioned, the dilatation balloon is inflated one or more times with liquid to a predetermined size at relatively high pressures, e.g. up to 20 atmospheres or more, to expand the arterial passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
In essentially all PTCA procedures, a guiding catheter having a preshaped distal tip is first percutaneously introduced into the cardiovascular system of a patient by a conventional Seldinger technique and advanced therein until the preshaped distal tip of the guiding catheter is disposed within the ascending aorta adjacent to the ostium of the desired coronary artery. The guiding catheter is twisted or torqued from its proximal end, which extends out of the patient, to guide the distal tip of the guiding catheter into the desired coronary ostium. Once the guiding catheter is in proper position within the patient's vasculature, the dilatation catheter is positioned within the inner lumen of the guiding catheter with a guidewire slidably disposed within an inner lumen of the dilatation catheter. The guidewire is first advanced out the distal tip of the guiding catheter seated in the coronary ostium into the patient's coronary artery and directed to the region of the patient's coronary anatomy where the procedure is to occur. A torque is applied to the proximal end of the guidewire, which extends out of the proximal end of the guiding catheter, to guide the curved or otherwise shaped distal end of the guidewire into a desired branch of the coronary artery. The advancement of the guidewire within the selected artery continues until it crosses the lesion to be dilated. The dilatation catheter is then advanced over the previously advanced guidewire, until the balloon on the distal extremity of the dilatation catheter is properly positioned across the lesion which is to be dilated.
With rapid exchange type catheters, which have relatively short guidewire receiving inner lumens in their distal extremities, The guidewire is first advanced through the guiding catheter and out into the coronary anatomy until the distal end of the guidewire is disposed beyond the stenotic site in the patient's coronary artery. The rapid exchange type catheter is then advanced over the guidewire until the balloon is properly disposed within the stenotic site where the dilatation is to occur.
It is conventional practice to fold the deflated balloon about the tubular inner member of the catheter and then advance a protective sheath with an inner diameter larger than the outer diameter of the folded balloon over the folded balloon to hold the balloon in the folded condition for subsequent packaging and sterilization. In addition to protecting the balloon in storage and transit, the sheath holds the folded balloon in position so that, when sterilized at elevated temperatures, the balloon is heat set in the folded condition. A folded balloon presents a much smaller profile than an unfolded balloon and thus is more easily advanced thorough a patient's vascular system. Moreover, being heat set in the folded condition, the balloon returns to the folded condition when subjected to a vacuum after being inflated, such as when venting air from the interior of the balloon and catheter. To facilitate advancing the protective sheath over a folded balloon the sheath is frequently formed of a lubricous fluoropolymer material. Unfortunately, the fluoropolymer protective sheath is usually quite hard and it does not conform to the shape of the folded balloon, so care must be exercised in advancing the sheath over the folded balloon on the catheter and in subsequent handling so that the balloon is not damaged by the protective sheath.
Protective sheaths are described in numerous U.S. Patents, for example, U.S. Pat. No. 5,425,710 (Khair et al.), U.S. Pat. No. 5,033,007 (Euteneuer), U.S. Pat. No. 4,710,181 (Fuqua), U.S. Pat. No. 4,738,666 (Fuqua), U.S. Pat. No. 4,540,404 (Wolvek), U.S. Pat. No. 5,066,298 (Hess), U.S. Pat. No. 5,116,318 (Hillstead) and U.S. Pat. No. 5,417,707 (Parkola). All of the above references are incorporated herein by reference.
While there have been much development effort in protective sheaths for balloons and catheters, none of the sheaths heretofore developed have been completely satisfactory. These prior sheaths have been either very difficult to slide over or otherwise apply to a folded balloon, or they have been difficult to remove from the balloon before the catheter is inserted into the patient. The present invention provides a protective sheath which eliminates or minimizes the problems of these prior sheaths.